Well, population density does that, I guess! Not much to be done about it, even in other parts of India with population not as crazily dense as Mumbai.
Between that and avoidable traffic jams created by vehicles blocking intersections, cycling may be the fastest method but also needs breathing more polluted air. But the time overhead of public transport can't be reduced with this population density. So ... a rock and a hard place!
I notice this sneaky snarkiness in reportage everywhere. The West's "progressiveness" is flaunted using per-capita nunbers, while the others' "backwardness" is backed up by absolute numbers. Flip the choice of numbers, and the whole picture flips!
All you need to know is whether the big per-capita polluters are driving down their consumption. And they are not, are they?